Insulated gate bipolar transistor and diode

ABSTRACT

A semiconductor device includes a semiconductor layer having a first principal surface on one side thereof and a second principal surface on the other side thereof, a channel region of a first conductivity type formed at a surface layer portion of the first principal surface of the semiconductor layer, an emitter region of a second conductivity type formed at a surface layer portion of the channel region in the semiconductor layer, a drift region of the second conductivity type formed in a region of the second principal surface side with respect to the channel region in the semiconductor layer so as to be electrically connected to the channel region, a collector region of the first conductivity type formed at a surface layer portion of the second principal surface of the semiconductor layer so as to be electrically connected to the drift region, a cathode region of the second conductivity type formed at a surface layer portion of the second principal surface of the semiconductor layer so as to be electrically connected to the drift region and including a continuously laid around line-shaped pattern, and a gate electrode formed at the first principal surface side of the semiconductor layer so as to face the channel region across an insulating film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device.

2. Description of the Related Art

A Reverse Conducting—Insulated Gate Bipolar Transistor (an RC-IGBT),which includes a diode and an IGBT, is disclosed in FIG. 2 of U.S.2010/276727.

The RC-IGBT includes a semiconductor layer. A p type channel region isformed at a surface layer portion of the semiconductor layer. An n typeemitter region is formed at a surface layer portion of the channelregion. An n type drift region is formed so as to be electricallyconnected to the channel region at a rear surface side of thesemiconductor layer with respect to the channel region of thesemiconductor layer.

At a surface layer portion of the rear surface of the semiconductorlayer, a p type collector region is formed so as to be electricallyconnected to the drift region. A plurality of n type cathode regions isformed so as to be electrically connected to the drift region at surfacelayer portions of the rear surface of the semiconductor layer. Theplurality of n type cathode regions is formed in a matrix pattern at therear surface of the semiconductor layer.

SUMMARY OF THE INVENTION

A preferred embodiment of the present invention provides a semiconductordevice that includes a semiconductor layer having a first principalsurface on one side thereof and a second principal surface on the otherside thereof, a channel region of a first conductivity type formed at asurface layer portion of the first principal surface of thesemiconductor layer, an emitter region of a second conductivity typeformed at a surface layer portion of the channel region in thesemiconductor layer, a drift region of the second conductivity typeformed in a region of the second principal surface side with respect tothe channel region in the semiconductor layer so as to be electricallyconnected to the channel region, a collector region of the firstconductivity type formed at a surface layer portion of the secondprincipal surface of the semiconductor layer so as to be electricallyconnected to the drift region, a cathode region of the secondconductivity type formed at a surface layer portion of the secondprincipal surface of the semiconductor layer so as to be electricallyconnected to the drift region and including a continuously laid aroundline-shaped pattern, and a gate electrode formed at the first principalsurface side of the semiconductor layer so as to face the channel regionacross an insulating film.

The above and other objects, features, and effects of the presentinvention will be made clear by the following description of thepreferred embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a semiconductor device according to a firstpreferred embodiment of the present invention.

FIG. 2 is partially cutaway perspective sectional view of a region IIshown in FIG. 1.

FIG. 3 is a circuit diagram of an electrical structure of thesemiconductor device shown in FIG. 1.

FIG. 4 is a bottom view of the semiconductor device shown in FIG. 1.

FIG. 5 is a bottom view of a semiconductor device according to areference example.

FIG. 6 is a graph obtained by simulation of a peak forward surge currenttolerance of the semiconductor device shown in FIG. 1.

FIG. 7 is a graph obtained by simulation of a collector current of thesemiconductor device shown in FIG. 1.

FIG. 8 is a graph obtained by simulation of a forward current of thesemiconductor device shown in FIG. 1.

FIG. 9 is a sectional view of a semiconductor device according to asecond preferred embodiment of the present invention.

FIG. 10 is a bottom view of the semiconductor device shown in FIG. 1 andshows a first modification example of a cathode region.

FIG. 11 is a bottom view of the semiconductor device shown in FIG. 1 andshows a second modification example of a cathode region.

FIG. 12 is a bottom view of the semiconductor device shown in FIG. 1 andshows a third modification example of a cathode region.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the conventional RC-IGBT disclosed in U.S. 2010/276727, asubstantially linear relationship is held between a total surface areaof the plurality of cathode regions and a peak forward surge currenttolerance. The peak forward surge current tolerance is defined as atolerance against a peak forward surge current I_(FSM).

That is, in a case where the total area of the plurality of cathoderegions is increased, the peak forward surge current toleranceincreases. Also, in a case where the total area of the plurality ofcathode regions is decreased, the peak forward surge current tolerancedecreases.

Therefore, in the conventional RC-IGBT, even if the total area of theplurality of cathodes is adjusted, the peak forward surge currenttolerance can only be adjusted within the linear relationship. It isthus difficult to adjust the peak forward surge current tolerancedeviating from the linear relationship and a design freedom is low.

A preferred embodiment of the present invention thus provides asemiconductor device capable of increasing design freedom and improvingthe peak forward surge current tolerance.

One preferred embodiment of the present invention provides asemiconductor device that includes a semiconductor layer having a firstprincipal surface on one side thereof and a second principal surface onthe other side thereof a channel region of a first conductivity typeformed at a surface layer portion of the first principal surface of thesemiconductor layer, an emitter region of a second conductivity typeformed at a surface layer portion of the channel region in thesemiconductor layer, a drift region of the second conductivity typeformed in a region of the second principal surface side with respect tothe channel region in the semiconductor layer so as to be electricallyconnected to the channel region, a collector region of the firstconductivity type formed at a surface layer portion of the secondprincipal surface of the semiconductor layer so as to be electricallyconnected to the drift region, a cathode region of the secondconductivity type formed at a surface layer portion of the secondprincipal surface of the semiconductor layer so as to be electricallyconnected to the drift region and including a continuously laid aroundline-shaped pattern, and a gate electrode formed at the first principalsurface side of the semiconductor layer so as to face the channel regionacross an insulating film.

According to the semiconductor device, the collector region of the firstconductivity type and the cathode region of the second conductivity typeare formed at the surface layer portion of the second principal surfaceof the semiconductor layer. In this structure, the collector regionincludes the line-shaped pattern continuously laid around the surfacelayer portion of the second principal surface of the semiconductorlayer. According to the cathode region having such an arrangement, thepeak forward surge current tolerance can be adjusted deviating from anarea of the cathode region.

That is, the peak forward surge current tolerance can be increased whiledeviating from the linear relationship between the area of the cathoderegion and the peak forward surge current tolerance held in theconventional RC-IGBT. Further, the peak forward surge current tolerancecan be adjusted by adjusting a region in which the cathode region islaid around at the second principal surface of the semiconductor layer.The design freedom can thus be increased.

The preferred embodiment of the present invention shall now be describedin detail with reference to the attached drawings.

FIG. 1 is a plan view of a semiconductor device 1 according to a firstpreferred embodiment of the present invention.

The semiconductor device 1 is a switching device that includes a ReverseConducting—Insulated Gate Bipolar Transistor (an RC-IGBT). The RC-IGBTincludes an IGBT and a free wheeling diode.

Referring to FIG. 1, the semiconductor device 1 includes a semiconductorsubstrate 2 as an example of a semiconductor layer. The semiconductorsubstrate 2 maybe an FZ substrate (Floating Zone substrate) that is madeof silicon and is formed by an FZ method. The semiconductor substrate 2is formed in a chip shape of quadrilateral shape in plan view.

The semiconductor substrate 2 includes a front surface 2 a, a rearsurface 2 b positioned on a side of the front surface 2 a, and sidesurfaces 2 c connecting the front surface 2 a and the rear surface 2 b.An active region 3 and an outer region 4 are set in the semiconductorsubstrate 2.

The active region 3 is a region in which a portion of the IGBT and aportion of the freewheeling diode are formed. The active region 3 is setin an inner region of the semiconductor substrate 2. The active region 3is set to a quadrilateral shape parallel to the respective side surfaces2 c of the semiconductor substrate 2 in plan view.

The outer region 4 is a region at an outer side of the active region 3.The outer region 4 is formed in a quadrilateral annular shapesurrounding the active region 3 in plan view.

A front surface electrode 5 is formed at the front surface 2 a of thesemiconductor substrate 2. The front surface electrode 5 supplieselectric power to the active region 3. The front surface electrode 5includes a gate electrode 6 and an emitter electrode 7.

The gate electrode 6 is formed along a periphery of the active region 3in plan view. More specifically, the gate electrode 6 includes gatefinger 8 and a gate pad 9.

The gate finger 8 is formed in the outer region 4 so as to surround theactive region 3. The gate finger 8 is formed in a quadrilateral annularshape extending along the respective side surfaces 2C of thesemiconductor substrate 2 in plan view.

The gate finger 8 may instead be formed along three side surfaces 2C ofthe semiconductor substrate 2 so as to define the active region 3 fromthree directions. The gate finger 8 may also cross the active region 3in accordance with the size of the active region 3.

The gate pad 9 is formed along one side surface 2C of the semiconductorsubstrate 2. The gate pad 9 is connected to the gate finger 8 at acentral portion in a length direction of the one side surface 2C of thesemiconductor substrate 2. The gate pad 9 is formed in a quadrilateralshape parallel to the respective side surfaces 2C of the semiconductorsubstrate 2 in plan view.

The gate pad 9 may instead be formed along a corner portion connectingtwo side surfaces 2C extending in mutually orthogonal directions. At thecorner portion, the gate pad 9 may be connected to two gate finger 8extending along mutually orthogonal directions. In a case where the gatefinger 8 includes a crossing portion that crosses the active region 3,the gate pad 9 may be connected to the crossing portion of the gatefinger 8.

An insulating region 10 is formed inside a region surrounded by the gateelectrode 6. The insulating region 10 is a region in which an electrodematerial is not present. The gate electrode 6 and the emitter electrode7 are insulated by the insulating region 10. The insulating region 10 isformed in a band shape extending along an inner edge of the gateelectrode 6. The insulating region 10 is formed in an endless shape(closed annular shape) in plan view in the present preferred embodiment.

The emitter electrode 7 covers the active region 3. The emitterelectrode 7 is formed in a region surrounded by the insulating region10.

FIG. 2 is a partially cutaway perspective sectional view of a region IIshown in FIG. 1.

Referring to FIG. 2, a p ⁻ type channel region 21 is formed at a surfacelayer portion of the front surface 2 a of the semiconductor substrate 2in the active region 3. The channel region 21 defines the active region3.

More specifically, the active region 3 is defined by a region surroundedby a peripheral edge of the channel region 21 in plan view. That is, theactive region 3 is a region where the channel region 21 is projectedonto the front surface 2 a and the rear surface 2 b of the semiconductorsubstrate 2.

An n⁻ type drift region 22 is formed at the rear surface 2 b side of thesemiconductor substrate 2 with respect to the channel region 21, in theactive region 3. The drift region 22 is electrically connected to thechannel region 21.

In the present preferred embodiment, an n⁻ type semiconductor substrateis used as the semiconductor substrate 2. That is, the drift region 22is formed using a portion of the semiconductor substrate 2.

A p⁺ type collector region 23 and an n⁺ type cathode region 24 areformed at a surface layer portion of the rear surface 2 b of thesemiconductor substrate 2, in the active region 3. The collector region23 and the cathode region 24 are exposed from the rear surface 2 b ofthe semiconductor substrate 2.

The collector region 23 and the cathode region 24 are electricallyconnected to the drift region 22, respectively. More specifically, thecollector region 23 and the cathode region 24 are electrically connectedto the drift region 22 via a buffer region 25. The buffer region 25 isformed so as to extend across a region between the drift region 22 andthe collector region 23 and a region between the drift region 22 and thecathode region 24.

An end portion of the cathode region 24 at the front surface 2 a side ofthe semiconductor substrate 2 is positioned inside the buffer region 25in regard to a thickness direction of the semiconductor substrate 2.That is, the cathode region 24 crosses a boundary of the collectorregion 23 and the buffer region 25. Specific structures of the collectorregion 23 and the cathode region 24 shall be described in detail later.

A plurality of trench gate structures 31 is formed at the surface layerportion of the front surface 2 a of the semiconductor substrate 2 in theactive region 3. Each of the trench gate structures 31 extends in a bandshape in plan view. Each of the trench gate structures 31 includes agate trench 32, a gate insulating film 33, and an embedded gateelectrode 34.

Each gate trench 32 is formed by digging the front surface 2 a of thesemiconductor substrate 2 toward the rear surface 2 b side. The gatetrench 32 penetrates the channel region 21. A bottom portion of the gatetrench 32 is positioned inside the drift region 22. The embedded gateelectrode 34 is embedded in the gate trench 32 across the gateinsulating film 33. The gate insulating film 33 covers the front surface2 a of the semiconductor substrate 2 as well.

n⁺ type emitter regions 35 are formed at surface layer portions of thechannel region 21. The emitter regions 35 are formed at sides of therespective trench gate structures 31. The emitter regions 35 are exposedfrom the front surface 2 a of the semiconductor substrate 2.

the n⁺ type emitter regions 35, the p⁻ type channel region 21, and then⁻ type drift region 22 are formed in that order from the front surface2 a side toward the rear surface 2 b side of the semiconductor substrate2 at sides of each trench gate structure 31.

The channel region 21 is shared by the trench gate structures 31. Theembedded gate electrodes 34 face the emitter regions 35, the channelregion 21, and the drift region 22 across the gate insulating films 33inside the gate trenches 32.

At the surface layer portion of the channel region 21, contact recessportions 41 are formed in respective regions between the trench gatestructures 31. Each contact recess portion 41 is formed in a band shapeextending along the trench gate structures 31 in plan view.

The contact recess portions 41 are formed by digging the front surface 2a of the semiconductor substrate 2 toward the rear surface 2 b side.Bottom portions of the contact recess portions 41 are positioned insidethe channel region 21. Side portions of the contact recess portions 41expose the emitter regions 35. A depth of the contact recess portion 41is less than a depth of each gate trench 32 (trench gate structure 31)in regard to the thickness direction of the semiconductor substrate 2.

In the channel region 21, p⁺ type contact regions 42 are formed inregions, each of which is oriented along the side portions and thebottom portion of a contact recess portion 41. The p⁺ type contactregions 42 are formed below the emitter regions 35. The contact regions42 have a p type impurity concentration that is higher than a p typeimpurity concentration of the channel region 21.

The emitter regions 35 may be exposed from entire side portions of thecontact recess portions 41. In this case, the contact regions 42 may beformed only in regions of the channel region 21 oriented along thebottom portions of the contact recess portions 41.

An insulating layer 43 is formed above the front surface 2 a of thesemiconductor substrate 2. The insulating layer 43 covers the trenchgate structures 31. The insulating layer 43 may have a laminatedstructure in which a plurality of insulating films is laminated. Theinsulating layer 43 may have a single layer structure constituted of asingle insulating film. The insulating layer 43 may include an oxidefilm (SiO₂) or a nitride film (SiN).

Contact holes 44 are formed in the insulating layer 43. The contactholes 44 expose the contact recess portions 41. The contact holes 44 arein communication with the contact recess portions 41. The contact holes44 are formed in band shapes extending along the same direction as thecontact recess portions 41 in plan view. Inner walls of the contactholes 44 are formed so as to be flush with respect to inner walls of thecontact recess portions 41.

The emitter electrode 7 is formed via a barrier metal layer 45 above theinsulating layer 43. The barrier metal layer 45 is a metal layerarranged to suppress diffusion of the emitter electrode 7 to outer sidesof the contact holes 44 and the contact recess portions 41.

The barrier metal layer 45 has a laminated structure including atitanium layer and a titanium nitride layer laminated in that order fromthe semiconductor substrate 2 side. The barrier metal layer 45 is formedin a film-like shape. More specifically, the barrier metal layer 45 isformed so that one surface and another surface facing each other areoriented along the inner walls of the contact recess portions 41, theinner walls of the contact holes 44, and the front surface of theinsulating layer 43.

The emitter electrode 7 fills the contact recess portions 41 and thecontact holes 44 and covers the front surface of the insulating layer43. Inside the contact recess portions 41, the emitter electrode 7 iselectrically connected via the barrier metal layer 45 to the channelregion 21, the emitter regions 35, the contact regions 42, etc.

The gate electrode 6 is formed at the insulating layer 43 across aninterval from the emitter electrode 7. The insulating region 10 (seealso FIG. 1), is formed by the insulating layer 43 exposed from theregion between the gate electrode 6 and the emitter electrode 7.

The trench gate structures 31 may be led out from the active region 3 toa region directly below the gate finger 8. The gate finger 8 maybeelectrically connected to the trench gate structures 31 via contactholes (not shown) formed in the insulating layer 43.

A collector electrode 46 as a rear surface electrode is formed at therear surface 2 b side of the semiconductor substrate 2. The collectorelectrode 46 is electrically connected to the collector region 23 andthe cathode region 24.

FIG. 3 is a circuit diagram of the electrical structure of thesemiconductor device 1 shown in FIG. 1.

Referring to FIG. 3, the semiconductor device 1 has a structure where anIGBT and a free wheeling diode are incorporated in the semiconductorsubstrate 2 in common. The free wheeling diode is formed by a pnjunction portion between the channel region 21 and the drift region 22.

The free wheeling diode includes the channel region 21 as an anoderegion. The free wheeling diode also includes the drift region 22 as acathode region. The free wheeling diode is electrically connected to theemitter electrode 7 via the channel region 21 and is electricallyconnected to the collector electrode 46 via the cathode region 24.

The semiconductor device 1 thus has a structure where the anode of thefreewheeling diode is electrically connected to the emitter electrode 7of the IGBT and the cathode of the freewheeling diode is electricallyconnected to the collector electrode 46 of the IGBT.

The specific arrangement of the cathode region 24 shall now be describedwith reference to FIG. 4. FIG. 4 is a bottom view of the semiconductordevice 1 shown in FIG. 1. For clarification, the cathode region 24 isshown with cross hatching in FIG. 4.

Referring to FIG. 4, in the present preferred embodiment, the collectorregion 23 is formed in a shape substantially matching a shape of theactive region 3 (that is, the shape of the channel region 21) in planview.

The cathode region 24 includes a line-shaped pattern that iscontinuously laid around in the active region 3. The cathode region 24has an n type impurity concentration that is higher than a p typeimpurity concentration of the collector region 23 in the presentpreferred embodiment. The cathode region 24 is formed in the activeregion 3 so that the p type impurity of the collector region 23 isoffset by the n type impurity.

A first region 50 and a second region 51 are set in the active region 3.The first region 50 is a region in which only the collector region 23 isformed. The second region 51 is a region in which both the collectorregion 23 and the cathode region 24 are formed. That is, the secondregion 51 is a region in which both the IGBT and the free wheeling diodeare formed.

The first region 50 is set along a peripheral edge portion of thesemiconductor substrate 2. More specifically, the first region 50 isformed along one side surface 2C of the semiconductor substrate 2. Evenmore specifically, the first region 50 is set in a region positioneddirectly below the gate pad 9 in the rear surface 2 b of thesemiconductor substrate 2.

The first region 50 faces the gate pad 9 in regard to the thicknessdirection of the semiconductor substrate 2. The first region 50 faces aregion overlapping o the active region 3 in the gate pad 9. A peripheraledge of the first region 50 may surround a peripheral edge of the regionoverlapping to the active region 3 in the gate pad 9 in plan view. Thefirst region 50 may be a region defined to have a quadrilateral shape inplan view.

The second region 51 is set in a region outside the first region 50 inthe active region 3. The second region 51 is defined to have a recessedshape in plan view. Even more specifically, the second region 51 is setin a region positioned directly below the emitter electrode 7 in therear surface 2 b of the semiconductor substrate 2. The second region 51faces the emitter electrode 7 in regard to the thickness direction ofthe semiconductor substrate 2.

In the following, a +X direction, a −X direction, a +Y direction, and a−Y direction shown in FIG. 4 may be used for convenience of description.The +X direction and the −X direction are two directions oriented alongone side of the semiconductor substrate 2 and shall be referred tosimply as the “X direction” when referred to collectively. The +Ydirection and the −Y direction are two directions oriented along anotherside of the semiconductor substrate 2 orthogonal to the one side andshall be referred to simply as the “Y direction” when referred tocollectively. In the present preferred embodiment, the X direction isalso a direction in which the gate pad 9 is led out from the gate finger8.

The cathode region 24 is formed in a non-uniform pattern (a non-uniformarrangement) in the active region 3. More specifically, the cathoderegion 24 is formed in the second region 51 and is thereby formed in aregion that does not face the gate pad 9 in the rear surface 2 b of thesemiconductor substrate 2.

The cathode region 24 includes a line-shaped pattern that is laid aroundcontinuously in a meandering form in the second region 51 in plan view.More specifically, the cathode region 24 includes a plurality of firstlines 52 and a plurality of second lines 53.

The plurality of first lines 52 extends along the X direction and isformed at intervals along the Y direction.

The plurality of first lines 52 includes a plurality of first lines 52A,a plurality of first lines 52B, and a plurality of first lines 52C.

The plurality of first lines 52A is formed in a region at a +Y directionend portion side in the active region 3. The plurality of first lines52B is formed in a region at a −Y direction end portion side in theactive region 3. The plurality of first lines 52C is formed in a regionbetween the first lines 52A and the first lines 52B in the active region3.

The plurality of first lines 52A is led out to a +Y direction sideregion with respect to the first region 50 (gate pad 9) in the activeregion 3. The plurality of first lines 52B is led out to a −Y directionside region with respect to the first region 50 (gate pad 9) in theactive region 3. The plurality of first lines 52A and the plurality offirst lines 52B face each other in the Y direction across the firstregion 50 (gate pad 9) in plan view. The plurality of first lines 52C isformed in a region facing the first region 50 (gate pad 9) along the Xdirection in the active region 3.

A length of each first line 52A and a length of each first line 52B aresubstantially equal in regard to the X direction, in the presentpreferred embodiment. A length of each first line 52C is less than thelength of each first line 52A and the length of each first line 52B inregard to the X direction.

The plurality of second lines 53 extends in the Y direction and connectsthe first lines 52 that is mutually adjacent in the Y direction. Thesecond lines 53 include a plurality of second lines 53A and a pluralityof second lines 53B.

Each of the second lines 53A connects +X direction end portions of twofirst lines 52 that are mutually adjacent along the Y direction. Each ofthe second lines 53B connects −X direction end portions of two firstlines 52 that are mutually adjacent along the Y direction. The pluralityof second lines 53A and the plurality of second lines 53B are formedalternately along the Y direction.

The cathode region 24 is thus formed in the line-shaped pattern ofcontinuously connected meandering form in plan view. Also, the cathoderegions 24 include the first lines 52A, 52B, and 52C that respectivelydiffer in the length in the X direction. The cathode region 24 isthereby formed in the pattern that is non-uniform with respect to theactive region 3.

A line width of the cathode region 24 defined by a Y direction width ofthe first line 52 and an X direction width of the second line 53 may beequal to or greater than 1 μm and equal to less than 100μm. The linewidth of the cathode region 24 is preferably equal to or greater than 10μm and equal to or less than 50 μm.

The cathode region 24 may have a uniform line width. The cathode region24 may have a line width that is not uniform. The cathode region 24 mayhave the first lines 52A, 52B, 52C that respectively differ in Ydirection width. The cathode region 24 may have the second lines 53A,53B that respectively differ in X direction width.

A ratio S₁/S_(A) of an area S₁ of the first region 50 with respect to anarea S_(A) of the active region 3 is, for example, equal to or greaterthan 0.03 (3%) and equal to or less than 0.3 (30%).

A ratio S_(K)/S_(A) of an area of the cathode region 24 with respect tothe area S_(A) of the active region 3 is less than a ratio S_(C)/S_(A)of an area S_(C) of the collector region 23 with respect to the areaS_(A) of the active region 3. The ratio S_(K)/S_(A) shall be referred toas the “area ratio S_(K)/S_(A) of the cathode region 24” in thedescription that follows . Also, the ratio S_(C)/S_(A) shall be referredto as the “area ratio S_(C)/S_(A) of the collector region 23” in thedescription that follows.

The area ratio S_(K)/S_(A) of the cathode region 24 may be equal to orless than 0.1 (10%). The area ratio S_(K)/S_(A) of the cathode region 24is preferably equal to or greater than 0.01 (1%) and equal to or lessthan 0.07 (7%).

A semiconductor device 101 according to a reference example shown inFIG. 5 was prepared for comparison with electrical characteristics ofthe semiconductor device 1. FIG. 5 is a bottom view of the semiconductordevice 101 according to the reference example. In FIG. 5, the samereference numerals are applied to the same structures as those describedin the semiconductor device 1, and the descriptions thereof will beomitted.

Referring to FIG. 5, a plurality of cathode regions 24 is formed in theactive region 3 in the semiconductor device 101. Each of the cathoderegions 24 is formed in a circular shape in plan view.

The plurality of cathode regions 24 is formed in a uniform pattern. Morespecifically, the plurality of cathode regions 24 is formed in a matrixpattern at intervals along the X direction and the Y direction. Thecathode regions 24 are also formed in a region directly below the gatepad 9 in the semiconductor device 101.

FIG. 6 is a graph obtained by simulation of the peak forward surgecurrent I_(FSM) of the semiconductor device 1. In FIG. 6, an abscissaindicates the area ratio S_(K)/S_(A) of the cathode region 24 and anordinate indicates the peak forward surge current I_(FSM).

The peak forward surge current I_(FSM) is the peak value of a commercialsinusoidal current of not less than one cycle that is tolerated within arange in which a semiconductor device does not break down. The higherthe peak forward surge current I_(FSM) the better the tolerance of thesemiconductor device against the peak forward surge current I_(FSM)(hereinafter referred to simply as the “peak forward surge currenttolerance”).

A plotted point P1 and plotted points P2, P3, P4, P5 are shown in thegraph of FIG. 6. The plotted points P2, P3, P4, P5 are connected by anapproximation line L.

The plotted point P1 indicates the peak forward surge current I_(FSM)simulation result when the area ratio S_(K)/S_(A) of the cathode region24 is 0.037 (3.7%) in the semiconductor device 1.

The plotted points P2, P3, P4, P5 indicate the peak forward surgecurrent I_(FSM) simulation results when the area ratio S_(K)/S_(A) ofthe cathode regions 24 is 0.012 (1.2%), 0.019 (1.9%), 0.023 (2.3%),0.032 (3.2%), respectively, in the semiconductor device 101.

Referring to the approximation line L, the peak forward surge currentI_(FSM) decreases as the area ratio S_(K)/S_(A) of the cathode regions24 decreases in the semiconductor device 101. On the other hand, thepeak forward surge current I_(FSM) increases as the area ratioS_(K)/S_(A) of the cathode regions 24 increases in the semiconductordevice 101.

The approximation line L of the semiconductor device 101 thus shows asubstantially linear relationship held between the area S_(k) of theplurality of cathodes 24 and the peak forward surge current I_(FSM).

However, the peak forward surge current I_(FSM) of the semiconductordevice 101 is equal to or less than 300 A and is a relatively smallvalue in all cases of the area ratio S_(K)/S_(A) of the cathode regions24.

Referring to the approximation line L, it may be considered that asatisfactory peak forward surge current I_(FSM) can be realized in acase where the area ratio S_(K)/S_(A) of the cathode regions 24 is madeclose to “1” in the semiconductor device 101.

However, in actuality, as the area ratio S_(K)/S_(A) of the cathoderegions 24 is made closer to “1”, the area ratio S_(C)/S_(A) of thecollector region 23 becomes closer to “0” and the function as the IGBTis thus lost. Therefore, even if the area ratio S_(K)/S_(A) of thecathode regions 24 is varied to vary the area S_(k) of the plurality ofcathodes 24, the peak forward surge current I_(FSM) can consequently beadjusted only within the linear relationship.

Therefore, it is difficult to obtain a relatively high peak forwardsurge current I_(FSM) in the semiconductor device 101. Even if theplurality of cathode regions 24 is formed in a quadrilateral shape orother polygonal shape in plan view instead of the circular shape, thesame problem arises.

Referring to the plotted point P1, according to the semiconductor device1, the peak forward surge current I_(FSM) of equal to or greater than1000 A is realized. That is, the semiconductor device 1 has the peakforward surge current I_(FSM) in a relatively high region deviating fromthe linear relationship held in the semiconductor device 101.

From the above results, it was understood that the relatively high peakforward surge current I_(FSM) can be realized deviating from theapproximation line L by forming the cathode region 24 including thecontinuous line-shaped pattern.

FIG. 7 is a graph obtained by simulation of a collector current I_(C) ofthe semiconductor device 1 shown in FIG. 1. In FIG. 7, an abscissaindicates a collector-emitter voltage V_(CE) and an ordinate indicatesthe collector current I_(C).

Characteristics of the collector current I_(C) when the semiconductordevice 1 is operated as the IGBT by applying the collector-emittervoltage V_(CE) between the collector electrode 46 and the emitterelectrode 7 are shown in FIG. 7.

Generally, according to a semiconductor device including an RC-IGBT,there is a possibility of occurrence of a snap-back phenomenon when acollector-emitter voltage V_(CE) of relatively small value (for example,within a range of equal to or greater than 0V and equal to or less than2.5V) is applied.

As shown in FIG. 7, according to the semiconductor device 1, occurrenceof the snap-back phenomenon is suppressed even when a collector-emittervoltage V_(CE) of relatively small value is applied. The reason for thisis considered to be because the first region 50 having the relativelylarge area that includes only the collector region 23 is formed in theactive region 3.

From the above results, it was understood that the semiconductor device1 can be stably operated as the IGBT even when the cathode region 24including the continuous line-shaped pattern is formed.

FIG. 8 is a graph obtained by simulation of a forward current I_(F) ofthe semiconductor device 1 shown in FIG. 1. In FIG. 8, an abscissaindicates a forward voltage V_(F) and an ordinate indicates the forwardcurrent I_(F).

Characteristics of the forward current I_(F) when the semiconductordevice 1 is made to operate as a free wheeling diode by applying theforward voltage V_(F) between the collector electrode 46 and the emitterelectrode 7 are shown in FIG. 8.

Referring to FIG. 8, it was understood that the semiconductor device 1can be stably operated as a free wheeling diode even when the cathoderegion 24 including the continuous line-shaped pattern is formed.

As described above, the semiconductor device 1 has the cathode region 24that includes the continuously laid around line-shaped pattern at thesurface layer portion of the rear surface 2 b of the semiconductorsubstrate 2. Therefore, in the semiconductor device 1, the peak forwardsurge current I_(FSM) of relatively high value can be set deviating fromthe approximation line L that the semiconductor device 101 according tothe reference example has.

Further, the peak forward surge current I_(FSM) can be adjusted easilyby adjusting the region in which the cathode region 24 is laid aroundwithin the active region 3 (second region 51) at the rear surface 2 bside of the semiconductor substrate 2. The design freedom can thus beincreased.

Consequently, the semiconductor device 1 capable of increasing thedesign freedom and improving the peak forward surge current tolerance.

FIG. 9 is a sectional view of a semiconductor device 61 according to asecond preferred embodiment of the present invention. In FIG. 9, thesame reference numerals are applied to the same structures as thosedescribed in the semiconductor device 1, and the descriptions thereofwill be omitted.

Referring to FIG. 9, the channel regions 21 are formed at intervals atthe surface layer portion of the front surface 2 a of the semiconductorsubstrate 2. The emitter region 35 is formed at the surface layerportion of each channel region 21. The emitter region 35 is formed atintervals from a peripheral edge of the channel region 21 to an innerside.

The drift region 22 is formed in a region at the rear surface 2 b sideof the semiconductor substrate 2 with respect to the channel regions 21.The drift region 22 is also formed in regions between the channelregions 21 mutually adjacent. The drift region 22 is electricallyconnected to the channel regions 21.

The collector region 23 and the cathode region 24 are formed at thesurface layer portion of the rear surface 2 b of the semiconductorsubstrate 2. The collector region 23 and the cathode region 24 areelectrically connected to the drift region 22 via the buffer region 25.The collector region 23 and the cathode region 24 have the samearrangements as in the first preferred embodiment.

A planar gate structure 62 is formed at the front surface 2 a of thesemiconductor substrate 2. The planar gate structure 62 has a laminatedstructure in which a gate insulating film 63 and a gate electrode 64 arelaminated in that order from the front surface 2 a side of thesemiconductor substrate 2.

The gate electrode 64 faces at least the channel regions 21 across thegate insulating film 63. More specifically, the gate electrode 64 facesthe emitter regions 35, the channel regions 21, and the drift region 22across the gate insulating film 63.

The contact regions 42 are formed in regions opposite sides from thegate electrode 64 with respect to the emitter regions 35 in the surfacelayer portions of the channel regions 21.

The active region 3 is defined by a region in which a plurality of unitcells 66 is formed in the present preferred embodiment. Each unit cell66 is a region in which two channel regions 21 are formed with respectto one planar gate structure 62.

The insulating layer 43 is formed at the front surface 2 a of thesemiconductor substrate 2. The insulating layer 43 covers the planargate structure 62. A contact hole 65 is formed in the insulating layer43. The contact hole 65 exposes the channel regions 21 and the emitterregions 35.

The emitter electrode 7 is formed above the insulating layer 43 acrossthe barrier metal layer 45. The emitter electrode 7 enters into thecontact hole 65 from above the insulating layer 43. Inside the contacthole 65, the emitter electrode 7 is electrically connected to thechannel regions 21, the emitter regions 35, and the contact regions 42.

According to the semiconductor device 61, the same effects as theeffects described above in the first preferred embodiment can beexhibited.

Although preferred embodiments of the present invention have beendescribed above, the present invention may be implemented in yet othermodes.

In the first preferred embodiment described above, the cathode region 24that includes a pattern of any of FIG. 10 to FIG. 12 may be formed inplace of the cathode region 24 that includes the line-shaped patternextending in a meandering manner.

FIG. 10 is a bottom view of the semiconductor device 1 shown in FIG. 1and shows a first modification example of the cathode region 24. In FIG.10, the same reference numerals are applied to the same structures asthose described in the semiconductor device 1, and the descriptionsthereof will be omitted. For clarification, the cathode region 24 isshown with cross hatching in FIG. 10.

Referring to FIG. 10, the cathode region 24 includes a plurality offirst lines 52 and a plurality of second lines 53. The plurality offirst lines 52 extends along the X direction and is formed at intervalsalong the Y direction. The plurality of second lines 53 extends in the Ydirection and connects the first lines 52 that are mutually adjacent inthe Y direction.

In the cathode region 24, the lengths of the first lines 52A, 52B arerespectively substantially equal to the length of the first lines 52C inregard to the X direction. The plurality of first lines 52A and theplurality of first lines 52B thus do not face each other in the Ydirection across the first region 50 (gate pad 9) in plan view.

The cathode region 24 is thereby localized in a region at the +Xdirection side of the active region 3. The first region 50 is formed ina rectangular shape extending along the Y direction in plan view in aregion at the −X direction side of the active region 3.

The cathode region 24 according to the present modification example isthus localized in a non-uniform pattern in the region at the +Xdirection side of the active region 3. Even when the semiconductordevice 1 has the cathode region 24 of such structure, the same effectsas the effects described in the first preferred embodiment can beexhibited. The cathode region 24 according to the present modificationexample may also be applied to the second preferred embodiment describedabove.

FIG. 11 is a bottom view of the semiconductor device 1 shown in FIG. 1and shows a second modification example of the cathode region 24. InFIG. 11, the same reference numerals are applied to the same structuresas those described in the semiconductor device 1, and the descriptionsthereof will be omitted. For clarification, the cathode region 24 isshown with cross hatching in FIG. 11.

Referring to FIG. 11, the cathode region 24 includes a plurality offirst lines 52 and a plurality of second lines 53. The plurality offirst lines 52 extends along the X direction and is formed at intervalsalong the Y direction.

The plurality of second lines 53 extends in the Y direction and connectsthe first lines 52 that is mutually adjacent in the Y direction. Each ofthe second lines 53 connects the +X direction end portions of two firstlines 52 that are mutually adjacent along the Y direction in the cathoderegion 24 according to the present modification example.

The cathode region 24 according to the present modification example thusincludes a line-shaped pattern of comb teeth form in plan view and isformed in a non-uniform pattern in the active region 3. The same effectsas the effects described with the first preferred embodiment can beexhibited even when the semiconductor device 1 has the cathode region 24of such structure. The cathode region 24 according to the presentmodification example may also be applied to the second preferredembodiment described above.

FIG. 12 is a bottom view of the semiconductor device 1 shown in FIG. 1and shows a third modification example of the cathode region 24. In FIG.12, the same reference numerals are applied to the same structures asthose described in the semiconductor device 1, and the descriptionsthereof will be omitted. For clarification, the cathode region 24 isshown with cross hatching in FIG. 12.

The gate pad 9 is formed at a central portion of the semiconductorsubstrate 2 in plan view in the present modification example. The firstregion 50 is thus set at a central portion of the active region 3 inplan view. The first region 50 is formed in a quadrilateral shape inplan view. The second region 51 is set to a quadrilateral annular shapesurrounding the first region 50.

The cathode region 24 includes a plurality of first lines 52 and aplurality of second lines 53. The plurality of first lines 52 extendsalong the X direction and is formed at intervals along the Y direction.The plurality of second lines 53 extends in the Y direction and connectsthe first lines 52 that are mutually adjacent in the Y direction.

The cathode region 24 according to the present modification exampleincludes a line-shaped pattern of spiral form formed by the plurality offirst lines 52 and the plurality of second lines 53. The cathode region24 according to the present modification example is formed in aquadrilateral spiral from parallel to the respective side surfaces 2 cof the semiconductor substrate 2 in plan view.

The cathode region 24 may be formed instead to a circular spiral form inplan view. The cathode region 24 may also be formed in an octagonalspiral form or other spiral form of polygonal shape besides aquadrilateral in plan view.

The cathode region 24 according to the present modification example isthus localized in a non-uniform pattern in a region at peripheral edgeportion sides of the active region 3. The same effects as the effectsdescribed with the first preferred embodiment can be exhibited even whenthe semiconductor device 1 has the cathode region 24 of such structure.The cathode region 24 according to the present modification example mayalso be applied to the second preferred embodiment described above.

In each of the preferred embodiments described above, the cathode region24 may include a plurality of line-shaped patterns that is formed in aseparated from each other and extend continuously respectively. Theplurality of line-shaped patterns may have patterns that differ mutuallyin plan view. The plurality of line-shaped patterns may have mutuallyequal patterns.

For example, the cathode region 24 may include at least one type ofpattern among a first pattern formed in a meandering form in plan view,a second pattern formed in a comb teeth form in plan view, or a thirdpattern formed in a spiral form in plan view.

In each of the preferred embodiments described above, an example wasdescribed where the semiconductor substrate 2 manufactured by the FZmethod is adopted as an example of the semiconductor layer. However, thesemiconductor layer may include an epitaxial substrate in place of thesemiconductor substrate 2.

The epitaxial substrate may have a laminated structure including a p⁻type semiconductor substrate made of silicon and an n⁻ type epitaxiallayer made of silicon and formed above the semiconductor substrate byepitaxial growth.

In this case, the p⁻ type semiconductor substrate corresponds to thecollector region 23. Also, the epitaxial layer corresponds to the driftregion 22. In this case, the cathode region 24 is formed by implantationof an n type impurity into the p type semiconductor substrate (collectorregion 23).

An arrangement in which the conductivity types of the respectivesemiconductor portions are inverted may be adopted in each of thepreferred embodiments described above. That is, a p type portion may beof an n type and an n type portion may be of a p type.

The present application corresponds to Japanese Patent Application No.2016-134335 filed in the Japan Patent Office on Jul. 6, 2016, and theentire disclosure of this application is incorporated herein byreference.

While preferred embodiments of the present invention have been describedin detail above, these are merely specific examples used to clarify thetechnical contents of the present invention, and the present inventionshould not be interpreted as being limited only to these specificexamples, and the scope of the present invention shall be limited onlyby the appended claims.

What is claimed is:
 1. A semiconductor device comprising: asemiconductor layer having a first principal surface on one side thereofand a second principal surface on the other side thereof; a channelregion of a first conductivity type formed at a surface layer portion ofthe first principal surface of the semiconductor layer; an emitterregion of a second conductivity type formed at a surface layer portionof the channel region in the semiconductor layer; a drift region of thesecond conductivity type formed in a region of the second principalsurface side with respect to the channel region in the semiconductorlayer so as to be electrically connected to the channel region; acollector region of the first conductivity type formed at a surfacelayer portion of the second principal surface of the semiconductor layerso as to be electrically connected to the drift region; a cathode regionof the second conductivity type formed at a surface layer portion of thesecond principal surface of the semiconductor layer so as to beelectrically connected to the drift region and including a line-shapedpattern continuously laid around, the line-shaped pattern including apattern extending in a meandering form as viewed in plan; and a gateelectrode formed at the first principal surface side of thesemiconductor layer so as to face the channel region across aninsulating film.
 2. The semiconductor device according to claim 1,wherein the cathode region is formed in non-uniform pattern at thesecond principal surface of the semiconductor layer.
 3. Thesemiconductor device according to claim 1, wherein the second principalsurface of the semiconductor layer has a first region where only thecollector region is formed, and a second region where the collectorregion and the cathode region are formed, and the first region is set ata peripheral edge portion of the second principal surface of thesemiconductor layer.
 4. The semiconductor device according to claim 1,wherein the second principal surface of the semiconductor layer has afirst region where only the collector region is formed, and a secondregion where the collector region and the cathode region are formed, andthe first region is set at a central portion of the second principalsurface of the semiconductor layer.
 5. The semiconductor deviceaccording to claim 1, further comprising a gate pad formed at the firstprincipal surface of the semiconductor layer so as to be electricallyconnected to the gate electrode, wherein the cathode region is formed ina region outside a region facing the gate pad in the second principalsurface of the semiconductor layer.
 6. The semiconductor deviceaccording to claim 1, wherein the line-shaped pattern of the cathoderegion includes a pattern extending in a comb teeth form as viewed inplan.
 7. The semiconductor device according to claim 1, wherein theline-shaped pattern of the cathode region includes a pattern extendingin a spiral form as viewed in plan.
 8. The semiconductor deviceaccording to claim 1, wherein the cathode region includes a first lineextending along a first direction, and a second line extending along asecond direction intersecting the first direction.
 9. The semiconductordevice according to claim 1, wherein the cathode region includes aplurality of first lines extending along a first direction and formed atintervals along a second direction intersecting the first direction, anda second line extending along the second direction and connected to thefirst lines adjacent mutually.
 10. The semiconductor device according toclaim 1, further comprising a collector electrode formed at the secondprincipal surface of the semiconductor layer and electrically connectedto the collector region and the cathode region.
 11. The semiconductordevice according to claim 1, wherein the semiconductor layer has anactive region, the collector region is formed in the active region, andthe cathode region is formed in the active region.
 12. The semiconductordevice according to claim 11, wherein a ratio S_(K)/S_(A) of an areaS_(K) of the cathode region with respect to an area S_(A) of the activeregion is less than a ratio S_(c)/S_(A) of an area S_(c) of thecollector region with respect to the area S_(A) of the active region.13. The semiconductor device according to claim 12, wherein the ratioS_(K)/S_(A) is equal to or less than 0.1.
 14. A semiconductor devicecomprising: a semiconductor layer having a first principal surface onone side thereof and a second principal surface on the other sidethereof; a channel region of a first conductivity type formed at asurface layer portion of the first principal surface of thesemiconductor layer; an emitter region of a second conductivity typeformed at a surface layer portion of the channel region in thesemiconductor layer; a drift region of the second conductivity typeformed in a region of the second principal surface side with respect tothe channel region in the semiconductor layer so as to be electricallyconnected to the channel region; a collector region of the firstconductivity type formed at a surface layer portion of the secondprincipal surface of the semiconductor layer so as to be electricallyconnected to the drift region; a cathode region of the secondconductivity type formed at a surface layer portion of the secondprincipal surface of the semiconductor layer so as to be electricallyconnected to the drift region and including a line-shaped patterncontinuously laid around, the line-shaped pattern including a patternextending in a comb teeth form as viewed in plan; and a gate electrodeformed at the first principal surface side of the semiconductor layer soas to face the channel region across an insulating film.
 15. Asemiconductor device comprising: a semiconductor layer having a firstprincipal surface on one side thereof and a second principal surface onthe other side thereof; a channel region of a first conductivity typeformed at a surface layer portion of the first principal surface of thesemiconductor layer; an emitter region of a second conductivity typeformed at a surface layer portion of the channel region in thesemiconductor layer; a drift region of the second conductivity typeformed in a region of the second principal surface side with respect tothe channel region in the semiconductor layer so as to be electricallyconnected to the channel region; a collector region of the firstconductivity type formed at a surface layer portion of the secondprincipal surface of the semiconductor layer so as to be electricallyconnected to the drift region; a cathode region of the secondconductivity type formed at a surface layer portion of the secondprincipal surface of the semiconductor layer so as to be electricallyconnected to the drift region and including a line-shaped patterncontinuously laid around, the line-shaped pattern including a patternextending in a spiral form as viewed in plan; and a gate electrodeformed at the first principal surface side of the semiconductor layer soas to face the channel region across an insulating film.